This enzyme is a type II chelatase, being either a monomer (CbiX) or a homodimer (CibK) and being ATP-independent. CbiK from Salmonella enterica uses precorrin-2 as the substrate to yield cobalt-precorrin-2. The enzyme contains two histidines at the active site that are thought to be involved in the deprotonation of the tetrapyrrole substrate as well as in metal binding. CbiX from Bacillus megaterium inserts cobalt at the level of sirohydrochlorin (factor-II) rather than precorrin-2.